The influence of agents which interact with the cholinergic receptor and/or with ionophores at endplates will be studied by using synaptic AChE activity as a probe. Drugs to be investigated will include cholinergic receptor ligands, antibiotics affecting membrane ion permeability and heavy metal ions. Similar experiments will be done on dystrophic muscles and at various stages of denervation on membrane fragments prepared from such muscles. Changes in isozyme patterns of membrane ChE's will be studied by micro disc electrophoresis and affinity chromatography. Isolation and purification of the complex from endplates containing AChE, drug binding protein and the membrane ionophore will be attempted. Mild methods of membrane dissociation, such as glycerol, osmotic shock and enzymes (phospholipase C, neuraminidase), followed by gradient centrifugation and gel permeation, will be used. Purified material, or membrane/endplate preparations, will be used to study the nature of the protein molecule which binds bisquaternary cholinergic drugs, its relation to the substrate site of AChE and the mechanism of regulation of substrate site activity. Quantitative changes in these parameters will be investigated in dystrophic and denervated muscle.